1. Field of the Invention
This invention relates to a drill bit having a drill head for cutting a hole in a direction forward from the drill head, sideways from the drill head and backwards from the drill head.
2. Description of the Prior Art
Drill bits for making non-linear holes are known, for example sold under the trade name xe2x80x9c3D BORRETxe2x80x9d, having an elongated shaft with a tool mount at a proximal end of the shaft and a drill head at the distal end of the shaft. The drill head has a plurality of flutes, which have a substantially straight front cutting edge substantially perpendicular to a longitudinal axis of the shaft. Further, the flutes have outer cutting edges, for cutting substantially perpendicularly to the shaft axis. Perceived disadvantages of this drill bit are the relative difficulty in machining the drilled hole in a rearward direction, with the forward direction being the initial drilling direction, and the relatively poor chip removal characteristics of the drill bit, caused by its flutes being substantially straight and parallel to the longitudinal axis of the shaft.
In the invention, a drill bit is provided which has a narrow shank, to facilitate sideways movement and tilting of a drill head in a drilled hole, without the shank making contact with the surfaces of the hole. The head is arranged on the drill bit at a distal end of the shank. The drill bit optionally has a generally elongate post arranged at a proximal end of the shank, for attaching the drill bit to a power or hand drill.
The head has a front portion, a rear portion and there-between a main body portion. A number of flutes extend radially from the main body portion and are arranged in a helical shape. Any number of flutes may be used, but advantageously four or six flutes are used. The flutes facilitate and speed up the chip removal from the bored hole. The front portion of the head has a central point, preferably connected to each flute via a tapered, preferably triangularly shaped, front cutting portion. The point is connected to at least one flute with the aforementioned front cutting portion. Each front cutting portion is provided with a front cutting edge, to form an initial cut in a workpiece, and to provide cutting capability in a forward direction.
At the distal end of the head, and arranged on at least one, but preferably two or all of the flutes, is a forward-facing roughing edge. The forward roughing edge makes a cut along the outer periphery of the bored hole.
Each flute has an outer cutting edge arranged on its outside edge. The outer cutting edges provide cutting ability in a direction sideways from the longitudinal direction of the drill bit.
At the proximal end of the head, and arranged on at least one, but preferably two or all of the flutes, is a rearward-facing roughing edge. The rearward roughing edge makes a cut along the outer periphery of the bored hole, when the drill bit is moved backwards in the bored hole.
The rear portion of the head is connected to at least one flute via a tapered, preferably triangularly shaped, rear cutting portion. Each rear cutting portion is provided with a rear cutting edge, to provide cutting capability in a direction substantially rearwards, i.e. for making cuts back towards the entering direction of the drill bit in the bored hole.
Thus, a non-linear hole may be drilled by advancing the drill bit into the work-piece, exerting lateral pressure as desired in order for the outer cutting edges to bite into the workpiece in a desired lateral direction, and possibly retracting the drill bit in such a way as to cause the rear cutting edges to bite into the workpiece, if desired.